Allows applications to use multiple parallel cursors when reading
all the documents from a collection, thereby increasing throughput.
The parallelCollectionScan command returns a document
that contains an array of cursor information.

Each cursor provides access to the return of a partial set of documents
from a collection. Iterating each cursor returns every document in the
collection. Cursors do not contain the results of the database command.
The result of the database command identifies the cursors, but does not
contain or constitute the cursors.